Staggered gear for bi-directional operation

ABSTRACT

A gear drive system for a printer designed to print upon a continuous roll of paper and having a blade used to cut off printed portions of paper from the paper roll is implemented. The gear drive system consists of a drive shaft 330, a slip clutch 401, a clutch gear 116, a fixed gear 110, and a staggered gear 112 which controls the paper cutter blade 106. During printing, clutch 401 allows the drive shaft 330 shaft to slip relative to the clutch gear 116. When printing stops, clutch 401 locks clutch gear 116 which is engaged with the first portion of staggered gear 112 and causes staggered gear 112 to rotate until the second portion of staggered gear 112 engages the fixed gear 110. Staggered gear 112 is then driven by the fixed gear 110. A cutter blade is controlled by staggered gear 112, with the blade cutting off the paper as the fixed gear 110 is in reverse rotation. After the paper is cut, fixed gear 110 resumes its forward rotation, rotating staggered gear 112 and consequently, rotating cutter blade 106 away from the paper. After the blade has been rotated, staggered gear 110 continues to turn, until the fixed gear disengages with the second portion of the staggered gear. Full torque is applied to both cutting and opening rotations of the cutter blade.

TECHNICAL FIELD

The invention relates in general to printers having geared drivesystems, and in particular to geared drive systems for printers thatoperate a cutter blade.

BACKGROUND INFORMATION

Printers may be classified as single-sheet printers or continuous-rollprinters. Single sheet printers include drive and handling means toadvance one sheet of paper at a time past a print head so thatcharacters may be printed thereon. As each sheet is printed, it isejected to be received by the user. Continuous-roll printers include aroll of paper instead of a supply of single sheets of paper. As the rollof paper is unrolled, the end of the paper is advanced past the printhead by feed rollers or other drive mechanism for printing. After aprinting job is completed, a blade or knife cuts the printed paper orthe paper is detached manually using a tear bar. Common continuous-rollprinters include thermal paper fax machines and retail checkoutregisters.

It is common to use a geared drive system in a continuous-roll printerwith a stepper motor as a power source. Typically, a stepper motor willturn a fixed number of degrees in response to a pulse of electricity ora command from a controller. Gears are used to connect the stepper motorto the drive mechanism to ensure that a fixed rotation translates to afixed advancement of the paper from the paper roll. It should be notedthat the use of a stepper motor is not required, as other power sourcesmay be used to control the rotation of the drive source and the feedrollers to accurately position the paper in relation to the print headfor precise printing.

When the stepper motor turns in the forward direction in acontinuous-roll printer, the paper is unwound from the paper roll andadvanced past the print head. Turning the stepper motor in the reversedirection engages the knife or cutter blade to cut the printed paperfrom the roll. Using the same motor for feeding paper through theprinter and cutting the printed paper is economical.

Continuous-roll printers are generally designed to only print in theforward direction. The paper is not retracted or wound back onto thepaper roll during or after printing. With a direct gear system,reversing the stepper motor results in reverse feeding of the paper.Therefore the stepper motor, when turning in reverse, decouples from thepaper drive system as it engages the cutter mechanism.

A wrap spring slip clutch, hereinafter referred to as a slip clutch,with an overrunning torque connects the gear drive system and the cutterblade. Slip clutches are used to transmit power in one direction ofrotation only (called the "locking rotation") and include teeth, ratchetor spring mechanisms that lock a driven part to a driving part when thedriven part is turned in the locking direction. When the rotation of thedriving part is reversed (called the "overrunning direction"), themechanism releases, causing the driven part to stop turning while thedriving part continues to turn, or "overrun" the driven part.

Some slip clutches are designed with an "overrunning torque" or amechanism that will not automatically release during reverse rotation. Aslip clutch with an overrunning torque will transmit torque from thedriven part to the driving part even in the reverse direction, but willslip if the torque required to drive the driven part exceeds theoverrunning torque.

As an example, consider a slip clutch with an overrunning torque of 1inch-ounce. This slip clutch will lock if driven in its lockingrotation, transmitting rotation of the driving part to the driven partwithout slippage. In the reverse rotation, the clutch will slip if theload on the driven part exceeds 1 inch-ounce. Causing the clutch toslip, however, requires an amount of torque equal to the overrunningtorque as a friction loss. In other words, a drive motor generating 10inch-ounces of torque in the reverse direction through a clutch that isslipping wastes 1 inch-ounce of torque that are required to cause theclutch to slip. The effective torque of the motor is thereby reduced to9 inch-ounces.

The slip clutch is configured so that a reverse rotation of the steppermotor causes a locking, or forward rotation of the slip clutch. When thestepper motor and gear drive are driven in reverse, the slip clutchlocks, engaging the cutter blade to slice off a piece of paper.Afterwards, the stepper motor resumes its forward rotation, causing theslip clutch to turn in reverse. The clutch, however, will not releaseuntil the torque required to continue turning the driven part exceedsthe overrunning torque. Therefore, the cutter blade will be lifted, asslip clutches can be designed to have an overrunning torque greater thanthe torque required to lift the cutting blade out of the paper path. Thecutter blade continues to lift until it reaches a stop or limitmechanism, preventing further rotation, greatly increasing the torquerequired to lift the blade, and causing the slip clutch to release.

Even after the blade is lifted and the clutch released the stepper motormust continue to expend energy overcoming the overrunning torque so theblade will not fall back into the paper path. The overrunning torque ofthe slip clutch is high compared to normal wrap spring clutches becausethe overrunning torque must be high enough to reliably open the cutterblades. Furthermore, the torque to open the cutter blade is limited tothe overrunning torque. This results in friction loss, is a waste ofenergy, and increases the cost of the printer because a larger steppermotor must be specified than is required to drive paper through thepaper path for printing. Additionally, it is rare that a slip clutch hasa constant overrunning torque during its lifetime because environmentalconditions, wear, and age modify the behavior of the clutch overtime. Ifthe overrunning torque becomes too high, paper will not feed properlybecause too much of the stepper motor's torque is wasted overcoming thefriction generated by the overrunning torque. If the overrunning torquebecomes too low, the cutter blade will not open or may slip back downinto the paper path during printing.

What is needed, therefore, is a device to allow a cutter blade to engageupon reverse rotation of the stepper motor, to disengage upon theconsequent forward rotation of the stepper motor in such a manner thatfull torque can be applied to both open and close the cutter blades, andto maintain its position out of the paper path during printing withoutadding the friction associated with an overrunning-style slip clutch tothe system.

One solution was disclosed in previously filed U.S. patent applicationSer. No. 08/919,749 for a clutchless drive system. However, theclutchless drive system depends on frictional forces to create thetorque required for engagement of the cutter blade upon reverse rotationof the cutter motor. Over time, these frictional forces might causewearing and maintenance problems. What is needed is a device thatensures that a positive engagement of the drive is engaged during theentire cycle, thereby eliminating the dependence on frictional forces.

SUMMARY OF THE INVENTION

The previously mentioned needs are fulfilled with the present invention.Accordingly, there is provided, in a first form, a staggered geardivided into two semi-circular portions which are staggered along thestaggered gear's rotational axis such that a first portion can be drivenby one gear during one part of a revolution and a second portion can bedriven by another gear at during another part of the revolution. Thestaggered gear is a member of a drive system for a printer including adrive gear connected to a drive shaft and includes a slip clutch capableof transmitting power through a clutch gear in one rotational directiononly wherein the drive shaft connects the slip clutch, clutch gear anddrive gear such that the clutch gear and the drive gear are adjacent toeach other, and the staggered gear is positioned so that it can bedriven by either the clutch gear or the drive gear. The staggered gearcontrols the printer cutter blade. Each portion of the staggered gearhas a section of starter teeth supported by a cantilevered section foreasing the transition between the clutch and drive gears.

The staggering of the two portions of the same gear allows the staggeredgear to be fully disengaged from the drive gear in one direction, andallows the staggered gear to be fully disengaged from the clutch in theother direction. Thus, full torque can be applied to the staggered gearin both directions to both close and open the cutter blades. Theapplication of full torque to the staggered gear results in the use of asmaller and more efficient motor saving power and cost. Additionally,the low overrunning torque increases the torque available to feed paper.

These and other features, and advantages, will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings. It is important to note the drawings arenot intended to represent the only form of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a printer incorporating one embodimentof the present invention;

FIG. 2A is a rear view of a related art gear drive mechanism typicallyfound in printers.

FIG. 2B is a perspective view of a gear drive mechanism in accordancewith the mechanism disclosed in FIG. 2A;

FIG. 3A is a front view of the dual plane clutch gear feature of oneembodiment of the present invention;

FIG. 3B is a back view of the dual plane clutch gear disclosed in FIG.3A;

FIG. 4 is a side view of the dual plane clutch gear mechanism disclosedin FIGS. 3A and 3B; and

FIG. 5 is a perspective view of the dual plane clutch gear mechanism ofone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The principles of the present invention and their advantages are bestunderstood by referring to the illustrated embodiment depicted in FIGS.1 and 3-5 of the drawings, in which like numbers designate like parts.In the following description, well-known elements are presented withoutdetailed description in order not to obscure the present invention inunnecessary detail. For the most part, details unnecessary to obtain acomplete understanding of the present invention have been omitted in asmuch as such details are within the skills of persons of ordinary skillin the relevant art. Details regarding control circuitry or mechanismsused to control the rotation of the various elements described hereinare omitted, as such control circuits are within the skills of personsof ordinary skill in the relevant art.

FIGS. 2A and 2B are a rear view and a perspective view of gear drivesystem 200 of related art typically used in printing devices. Motor gear202 is driven by a stepper motor 219 or other power source. Motor gear202 meshes with paper feed gears 203. Paper feed gears 203 drive feedrollers or another mechanism (not illustrated) to feed paper from a rollof paper through a paper path and past a print head for printing. Toprevent paper from being feed backwards during the cut cycle, paper feedgears 203 are decoupled from the paper feed rollers by either a one wayclutch or similar device. Clutch gear 204 is also driven by motor gear202. Clutch gear 204 transmits power through shaft 206 to slip clutch208. The output, or drive portion, of slip clutch 208 is attached toslip clutch gear 210. Slip clutch gear 210 drives cutter blade gear 212.Carried by cutter blade gear 212 is pin 214 which extends from cutterblade gear 212 at a point near cutter blade gear 212's perimeter.

Also illustrated in FIGS. 2A and 2B are cutter blade 216 and cutterblade bracket 218. Cutter blade bracket 218 is attached to one end ofcutter blade 216. Cutter blade bracket 218 has a slot (not illustrated)into which pin 214 extends. As cutter blade gear 212 rotates, pin 214causes cutter blade bracket 218 to rotate and cutter blade 216 to moveacross the paper in a cutting motion.

Slip clutch 208 is configured so that its locking rotation iscounterclockwise when viewed in FIG. 2B. When motor gear 202 is drivenclockwise, clutch gear 204 and shaft 206 turn in a counterclockwisedirection. This locks slip clutch 208, causing slip clutch gear 210 toturn counterclockwise. The counterclockwise motion of slip clutch gear210 causes a clockwise rotation of cutter blade gear 212. As cutterblade gear 212 rotates clockwise, pin 214 follows, driving blade bracket208 which rotates cutter blade 216 clockwise into the paper path to cutthe paper.

After the paper is cut, the stepper motor 219 or other drive sourcereverses rotation, which in turn reverses clutch gear 204 and shaft 206to a clockwise direction. Slip clutch 208 is configured with anoverrunning torque higher than the torque required to "unwind" cutterblade gear 212 and rotate cutter blade 216 counter-clockwise out of thepaper path. Cutter blade 216's counter-clockwise rotation is limited,however, by a stop or other limit device (not illustrated). Once cutterblade 216 reaches its limit of rotation, further rotation of cutterblade gear 212 and slip clutch gear 210 is impeded, however clutch gear204 and shaft 206 continue to rotate, causing slip clutch 208 to unlock.

The disadvantages presented by this arrangement are many. First, slipclutch 208 must be designed with an amount of overrunning torque socutter blade 216 will open in response to the "backwards"(counterclockwise) rotation of cutter blade gear 212. Additionally, slipclutch 208 must be designed with overrunning torque so cutter blade 216will not fall back into the paper path during printing or paper feeding.This overrunning torque acts as a drag on the motor or power source. Theenergy of the motor is ideally used to feed paper through the printer,and increasing the size of the motor to overcome the overrunning torqueof slip clutch 208 results in a waste of energy and increases motorcosts. Second, as the slip clutch wears, the overrunning torque maydecrease, which lessens the load on the motor, but tends to allow cutterblade 216 to fall to open. Finally, the overrunning torque may increaseover time, which will increase the load on the motor, decreasing themotor's ability to feed paper through the printer.

Turning now to FIG. 1, a printer 100 is illustrated incorporating oneembodiment of the present invention. A portion of the wall of printer100 has been removed to illustrate interior detail and a portion of theelements of the present invention. Printer 100 comprises drive motor 102which is used to feed paper 104 from a paper roll (not illustrated)along a paper path (not illustrated) for printing by a print head (notillustrated). The paper roll is stored inside printer 100. The portionof paper visible in FIG. 1 has been printed and is in a position to becut off by cutter blade 106. Cutter blade 106 is attached to cutterblade bracket 108. Cutter blade bracket 108 comprises a slot 109.Rotation and torque from motor 102 is transmitted by gearing 111 (only aportion of gearing 111 is visible) to fixed gear 110 which is rotatablyfixed to shaft 330. When printing is complete and the paper is to becut, motor 102 reverses engaging clutch gear 116 which causes dual planeclutch gear 112 to rotate until fixed gear 110 can engage dual planeclutch gear 112. Pin 114 is then carried by dual plane clutch gear 112.Pin 114 extends from dual plane clutch gear 112 at a point near dualplane clutch gear 112's perimeter. Pin 114 engages slot 109, so thatrotation of dual plane clutch gear 112 causes pin 114 to rotate cutterblade bracket 108, such that cutter blade 106 rotates a cut edge (notillustrated) across the paper path in a cutting motion.

Drive motor 102 is preferably a stepper motor, although any power sourcethat provides a controlled rotation may be used.

Printer 100 in FIG. 1 is only one embodiment of the present invention.Other embodiments may include fax machines using thermal paper, aprinter that uses a knife or cutter blade to cut a printed portion ofpaper away from a roll of paper, and the like.

Turning now to FIGS. 3A, 3B, 4, and 5, a front view, a back view, a sideview, and an isometric view of one embodiment of the present inventionare illustrated. The apparatus illustrated in FIGS. 3A, 3B, 4, and 5 isintended to replace slip clutch 208 and cutter blade gear 212 of FIGS.2A and 2B to overcome their inherent disadvantages. The apparatus inFIGS. 3A, 3B, 4 and 5 is also illustrated in FIG. 1 as installed inprinter 100.

FIG. 3A is a front view of dual plane or staggered gear 112. Staggeredgear 112 is divided into a first portion which is staggered with respectto a second portion along the rotational axis of the staggered gear 112.A perimeter of the first portion is divided into sections 303 and 304. Aperimeter of the second portion is divided into sections 301 and 302.First section 301 is comprised of gear teeth 305A, which are nonelasticand sized and spaced to mesh with the teeth of fixed gear 110. For thepurpose of this description and the following claims, the word"nonelastic" means stiff or not easily yielding under pressure orforces. Fixed gear 110 is obscured from this view by clutch gear 116because clutch gear 116 has substantially the same gear teeth height,pitch and spacing as fixed gear 110. Fixed gear 110 and clutch gear 116are coaxial. The teeth of slip clutch gear 116 and fixed gear 110 arealso nonelastic.

Second section 302 has starter teeth 306A. Starter teeth 306A arenonelastic and have the same spacing, or pitch, as gear teeth 305A butare shorter in height than gear teeth 305A to facilitate meshing betweenfixed gear 110 (not shown) and staggered gear 112. All of starter teeth306A are shorter in height than gear teeth 305A, however first startertooth 307 is the shortest, with each successively clockwise startertooth 306A taller than a preceding starter tooth 306A. Starter teeth306A are supported on a cantilever section attached to staggered gear112 near the transition between sections 301 and 302.

Third section 303 has starter teeth 306B which, as shown in FIG. 3A,mirror starter teeth 306A, but are in a different plane than starterteeth 306A. For the purpose of this description and the followingclaims, the word "plane" means the volume between two substantially flatand parallel imaginary surfaces. Starter teeth 306B are nonelastic andhave the same spacing, or pitch, as gear teeth 305A and 306A but areshorter in height than gear teeth 305A to facilitate meshing betweenclutch gear 116 and staggered gear 112. All of starter teeth 306B areshorter in height than gear teeth 305, however first starter tooth 309is the shortest, with each successively counterclockwise starter tooth306B taller than a preceding starter tooth 306B. Starter teeth 306B aresupported on a cantilever section attached to staggered gear 112 nearthe transition between sections 303 and 304.

Fourth section 304 is comprised of gearteeth 305B, which are nonelasticand substantially identical to gear teeth 305A, and sized and spaced tomesh with the teeth of spring clutch gear 116.

Three flat gear surfaces are shown in FIG. 3A because sections 301 and302 are staggered along staggered gear 112's rotational axis withrespect to sections 303 and 304. Gear surface 312 is closer to theviewer, gear surface 318 is the farther from the viewer, and gearsurface 311 lies between gear surface 312 and gear surface 318. Curvedsurface 310 is a transition surface between the gear surface 312 and thegear surface 311. Curved surface 310 is positioned such that it does notinterfere with the movement of pin 114 and the rotation of cutter bladebracket 108 (not shown), and there is enough material to structurallysupport the cantilevered supports for sections 303 and 304. Transitiongear surface 321 is shown as a semi-circular line because it isperpendicular to gear face 311 and gear face 318.

Sections 303 and 304 are in the first portion of staggered gear 112.Sections 303 and 304 lie in substantially the same plane and arepositioned to engage clutch gear 116. Sections 301 and 302 are in thesecond portion of staggered gear 112. Sections 302 and 301 lie in aplane farther from the viewer than sections 303 and 304. Sections 303and 304 are positioned such that gear teeth 305B and 306B mesh with theteeth of clutch gear 116.

FIG. 3B is a back view of staggered gear 112 showing sections, 301, 302,303 and 304. In this view, sections 303 and 304 are in a plane fartherfrom the viewer relative to sections 301 and 302. Two gear surfaces areshown in FIG. 3B. Transition gear surface 315 is shown as asemi-circular line because it is perpendicular to gear face 313 and gearface 314. Gear surface 314 is closer to the viewer than gear surface313.

First section 301 is comprised of gear teeth 305A. Second section 302has starter teeth 306A. Third section 303 has starter teeth 306B. Thefourth section 304 is comprised of gear teeth 305B. Because clutch gear116 is in a plane behind fixed gear 110, it is obscured from this viewby fixed gear 110. Thus, fixed gear 110 appears to be engaged withstaggered gear 112. Actually, fixed gear 110 is in a plane closer to theviewer than section 303 of staggered gear 112 and is not engaged withstaggered gear 112. Only clutch gear 116 is engaged with staggered gear112. Fixed gear 110 has substantially the same gear teeth height, pitchand spacing as clutch gear 116.

FIG. 4 is a side view of the staggered gear shown in FIGS. 3A and 3B.Gear surfaces 311, 312, 318, and 314 are perpendicular to the viewer andare seen as straight lines. The surfaces that are parallel to and can beseen from FIG. 3A are gear surface 312, gear surface 311, and gearsurface 318. Curved surface 310 and transition surface 321 are alsoshown. The surfaces that are parallel to and can be seen from FIG. 3Bare gear surface 314 and gear surface 313. Transition surface 315 isalso shown.

FIG. 4 also shows gear teeth 306B engaged in the teeth of a springclutch gear 116 which is mounted on shaft 330. For clarity, only part ofshaft 330 is shown in this view. Along the rotational axis, a firstplane or the first portion of staggered gear 112 can be defined as thatportion of the gear that lies between surface 312 and 311 andcorresponds to section 303 and 304 of FIGS. 3A and 3B. A second plane orthe section portion of staggered gear 112 can be defined as that portionof the gear that lies between surface 318 and 314 which corresponds tosections 301 and 302 of FIGS. 3A and 3B. Fixed gear 110 is shown suchthat it engages the second portion of staggered gear 112. Clutch gear116 is shown on shaft 330 such that it engages the first portion ofstaggered gear 112. Coupled with clutch gear 116 is a wrap spring clutch401. Slip clutches are used to transmit power in one direction ofrotation only (called the "locking rotation") and include teeth, ratchetor spring mechanisms that lock a driven part to a driving part when thedriven part is turned in the locking direction. When the rotation of thedriving part is reversed (called the "overrunning rotation"), themechanism releases, causing the driven part to stop turning while thedriving part continues to turn, or "overrun" the driven part. Springclutch 401 is readily available in the marketplace and well known tothose who practice the art of designing gear systems for paper printers.

FIG. 5 is an isometric drawing showing a partial view of cutter blade106 attached to cutter blade bracket 108. Cutter blade bracket 108 ispartially shown because it is obscured by staggered gear 112. Pin 114extends through a circular opening in staggered gear 112 to a slot (notshown) in cutter blade bracket 108. The gear teeth 306B of staggeredgear 112 are engaged in the teeth of a spring clutch gear 116. Alsoconnected to shaft 330 is spring clutch 401 and fixed gear 110. Shaft330 is driven by gearing 111 (partially shown) which is driven by motor102 (not shown).

OPERATION

The manner of using staggered gear 112 can be illustrated by showing itas a member of a gear assembly illustrated in FIGS. 5 and 3B.

In FIG. 3B, clockwise rotation of shaft 330 and fixed gear 110corresponds to normal printing and paper feeding of printer 100. Springclutch 401 is configured so that its overrunning rotation is clockwisewhen viewed in FIG. 3B. When the printer is feeding paper, spring clutchgear 116 mesh with gear teeth 305B or 306B. A stop (not shown) limitsthe rotation of staggered gear 112 such that spring clutch shaft 330spins freely relative to clutch gear 116 because spring clutch is beingdriven in the overrunning direction. Fixed gear 110 turns clockwise butdoes not engage staggered gear 112 because it is staggered and inanother plane relative to section 303 and 304. When printing iscompleted and the paper is to be cut by cutter blade 106, drive motor102 (FIG. 1) reverses, causing gearing 111 to turn shaft 330counterclockwise which causes clutch 401 to lock with clutch gear 116turning clutch gear 116 counterclockwise. Because clutch gear 116 is nolonger turning in the overrunning direction, clutch gear 116 causes aclockwise rotation in staggered gear 112. In the beginning of the cutcycle, the load on clutch gear 116 and staggered gear 112 is minimal. Asthe cutter starts to close, there is still minimal loads on staggeredgear 112. At this point in the cycle, a transition occurs where the lastteeth of 306B are starting to disengage with the spring clutch gear 116in one plane and the teeth of fixed gear 110 engaged starter teeth 306Ain another plane. Because starter teeth 306A are shorter than gear teeth305A, the gears tend to mesh easily without binding or locking. Bendingor locking is also eliminated because any mismatch between starter teeth306A and gear teeth 305A will flex the cantilever support to allow theteeth to mesh. Once staggered gear 112 has rotated to so that gear teeth305A of section 301 are fully engaged with the fixed gear teeth,staggered gear 112 is no longer engaged with the teeth of spring clutchgear 116. At this point in the cycle, full available torque can betransmitted from fixed gear 110 to staggered gear 112 in bothdirections. No power is lost overcoming an overrunning torque of aclutch because the clutch is no longer engaged with staggered gear 112.Another mechanism (not shown) such as spring clutch or similar devicedecouples the paper feed drive so that the paper is not fed backwardsduring the cut cycle. Such a device is common in the marketplace andwell known to those skilled in the art of designing printers.

After the paper has been cut, normal printing and paper feeding iscontinued. As such drive gear 111 returns to a clockwise rotation,causing staggered gear 112 to follow along in a counterclockwiserotation, opening cutter blade 106 out of the paper path after the paperhas been cut. In opening cutter blade 106, staggered gear 112 rotatescounterclockwise, with each successive gear tooth 305A meshing andunmeshing with fixed gear 110. As staggered gear 112 continues to rotatecounterclockwise another transition occurs where the starter teeth 306Adisengage with the teeth of fixed gear 110 and simultaneously thestarter teeth 306B begins engaging with the teeth of clutch gear 116.Because starter teeth 306B are shorter than gear teeth 305B, the gearstend to mesh easily without binding or locking.

Unlike the arrangements of the related art illustrated in FIGS. 2A and2B, wherein the torque to open blade 216 is limited by the slip torqueof slip clutch 208, all the available torque from drive gear 111 isapplied to open cutting blade 106. The full torque is available in boththe forward and reverse directions for the desired amount of rotationwhile disengaging the drive when the staggered gear 112 is rotated backto its initial position. As such, none of drive motor 102's energy islost on overcoming the overrunning torque of a slip clutch or similarsolutions. In the related art, the overrunning torque of slip clutch 208acts as a drag on the motor or power source and increases the size ofthe motor to overcome the torque resulting in a waste of energy.Additionally, as the slip clutch 208 wears, the overrunning torque maydecrease, which lessens the load on the motor, but tends to allow cutterblade 216 to fall to open. Finally, the overrunning torque of prior artmay increase over time, which will increase the load on the motor,decreasing the motor's ability to feed paper through the printer. Withthe present invention, there is minimal overrunning torque andconsequently, no additional load on the motor. As such, the motor can bemore efficient and reliable.

Although the invention has been described with reference to specificembodiments, these descriptions are not meant to be construed in alimiting sense. Various modifications of the disclosed embodiments, aswell as alternative embodiments of the invention will become apparent topersons skilled in the art upon reference to the description of theinvention. It is therefore, contemplated that the claims will cover anysuch modifications or embodiments that fall within the true scope of theinvention.

What is claimed is:
 1. A gear apparatus comprising:a first portionhaving a first peripheral surface capable of being driven about arotational axis by a first drive gear; and a second portion having asecond peripheral surface capable of being driven about said rotationalaxis by a second drive gear, said second portion is secured to saidfirst portion such that said first portion is contiguous with saidsecond portion and said first portion is staggered along said rotationalaxis with respect to said second portion such that each peripheralsurface are independently driveable, wherein a first section of saidfirst portion has a plurality of starter gear teeth of increasing heightwith a tallest tooth adjacent to a second section of said first portionand a first section of said second portion has a plurality of startergear teeth of increasing height with a tallest tooth adjacent to asecond section of said second portion.
 2. The apparatus of claim 1,wherein said second section of said first portion has a plurality ofgearteeth equal in height to said tallest tooth of said first sectionand said second section of said second portion has a plurality of gearteeth equal in height to said tallest tooth of said first section. 3.The apparatus of claim 2, wherein said gear teeth of each section arenon-elastic.
 4. The apparatus of claim 3, wherein said gear teeth ofsaid second section of said first portion is substantially identical inheight and spacing to said gear teeth in said second section of saidsecond portion.
 5. The apparatus of claim 1, wherein said first sectionof each portion is supported by a cantilevered member.
 6. The apparatusof claim 1, wherein said first drive gear and said second drive gear areadjacent gears coaxially connected by a drive shaft.
 7. The apparatus ofclaim 6, wherein one of the drive gears is a clutch gear and the othergear is a drive gear fixedly attached to said drive shaft and saidclutch gear is coupled to a slip clutch capable of transmitting power tosaid clutch gear in one rotational direction only.
 8. The apparatus ofclaim 7, wherein when said drive shaft is turning in a first rotationaldirection, said drive gear is not engaged with said first portion orsaid second portion and said clutch gear is engaged such that saidclutch gear is not urging said first portion to turn.
 9. The apparatusof claim 8, wherein when said drive shaft is turning in a secondrotational direction, said clutch locks said clutch gear thereby urgingsaid first portion to rotate until said fixed drive gear engages saidsecond portion and further rotates second portion until said clutch gearis no longer engaged with said first portion.
 10. A gear drive system,comprising:a drive gear connected to a drive shaft; a slip clutchcapable of transmitting power through a clutch gear in one rotationaldirection only; said drive shaft connecting said slip clutch, clutchgear and drive gear such that said clutch gear and said drive gear areadjacent to each other; and a staggered gear divided into two portionswhich are staggered along a rotational axis such that a first portioncan be driven by said clutch gear during part of a revolution withoutengagement of said drive gear and a second portion can be driven by saiddrive gear during another part of said revolution without engagement ofsaid clutch gear.
 11. The system of claim 10, where each portion of saidstaggered gear contains a first section and a second section along aperimeter of each portion and said first section of each portion has aplurality of equally-spaced starter teeth of increasing height with atallest tooth adjacent to said second section.
 12. The system of claim11, wherein said second section of each portion has a plurality ofequally-spaced gear teeth equal in height to said tallest tooth of saidfirst section.
 13. The system of claim 12, wherein said teeth arenon-elastic.
 14. The system of claim 12, wherein said first section ofeach portion is supported by a cantilevered member.
 15. A drive drivesystem for a printer comprising:a drive gear connected to a drive shaft;a slip clutch connected to said drive shaft such that a clutch gear isadjacent to said drive gear; a staggered gear having a first portionoffset from a second portion along its rotational axis, each portionhaving a section of gear teeth of substantially uniform height and asection of starter gear teeth with reduced height on a cantilevered armbiased towards a perimeter of said staggered gear; said clutch gearselectively pressed against one section of said first portion of saidstaggered gear to allow said clutch gear to remain stationary while saidstaggered gear remains at its limit of rotation in said first direction,wherein when said drive shaft reverses its rotational direction, saidstaggered gear turns less than one rotation in a second direction pastsaid first portion, as said drive gear successively engages said starterteeth of said second portion of said staggered gear and said gear teethof said drive gear turns said staggered gear less than one rotation; andsaid drive gear selectively pressed against said second portion of saidstaggered gear to allow said drive gear to turn in a second directionwhile said staggered gear turns less than a rotation in a thirddirection, wherein when said drive gear turns in said first direction,said staggered gear turns in a fourth direction past said second portionof said staggered gear as said clutch gear successively engages saidstarter teeth of said first portion of said staggered gear until saidlimits of said staggered gear's rotation is reached.
 16. The gear drivesystem of claim 15 further comprising a stepper motor, wherein power toturn said drive gear and said staggered gear is provided by said steppermotor.